URDF

#urdf   #robot_state_publisher   #urdf_to_graphiz  

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Table of Content

URDF

Unified Robot Description Format URDF is xml specification that describe robot physical as links and joints elements

• robot: The root element in a robot description file must be a robot
• link: The link element describes a rigid body with an inertia, visual features, and collision properties.
• joint: The joint element describes the kinematics and dynamics of the joint between two links
• gazebo: The gazebo element is an extension to the URDF robot description format, used for simulation purposes in the Gazebo simulator.

minimal urdf

<robot name="robot_name">
  <!--  robot links joints -->
</robot>

elements

• link
• joint
• gazebo
• more elements

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Tools to view and debug urdf

• rviz
• gazebo
• online urdf preview
• verification and Visualization

Install

sudo apt install ros-humble-urdf

Demo

demo.urdf

<?xml version="1.0" encoding="UTF-8"?>
<robot name="my_robot">
    <link name="base_link">
        <visual>
            <geometry>
                <cylinder length="0.6" radius="0.2" />
            </geometry>
        </visual>
    </link>
    <link name="link1">
        <visual>
            <geometry>
                <cylinder length="0.6" radius="0.2" />
            </geometry>
        </visual>
    </link>
    <joint type="fixed" name="base2link_joint">
    <origin xyz="1 0 0" rpy="0 0 0"/>
        <parent link="base_link"/>
        <child link="link1"/>
    </joint>
</robot>

gazebo cli

check urdf validation with gazebo cli

check using gazebo

gz sdf --check <file>

urdf_to_graphiz

urdf_to_graphiz <file>

# check the pdf output
evince my_robot.pdf

online preview

urdf

rviz

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch_ros.actions import Node

URDF = "basic_joint.urdf"
PACKAGE = "gazebo_tutorial_pkg"


def generate_launch_description():
    ld = LaunchDescription()

    pkg = get_package_share_directory(PACKAGE)
    urdf = os.path.join(pkg, "urdf", URDF)
    with open(urdf, "r", encoding="utf-8") as f:
        robot_description = f.read()

    robot_state_publisher = Node(
        package="robot_state_publisher",
        executable="robot_state_publisher",
        name="robot_state_publisher",
        output="screen",
        parameters=[{"robot_description": robot_description}]
    )

    joint_state_publisher_node = Node(
        package="joint_state_publisher_gui",
        executable="joint_state_publisher_gui",
        name="joint_state_publisher_gui",
    )

    rviz_node = Node(
            package='rviz2',
            namespace='',
            executable='rviz2',
            name='rviz2',
            arguments=['-d' + os.path.join(pkg, 'config', 'rviz.rviz')]
        )

    ld.add_action(robot_state_publisher)
    ld.add_action(joint_state_publisher_node)
    ld.add_action(rviz_node)
    return ld

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VSCode

Add urdf snippets with urdf extension

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Reference

• urdf